When asserting on equality using the EqualConstraint you may not always get the behaviour you want depending on what objects are being asserted on. This can be influenced by whether or not the objects are value or reference types and if the type implements or overrides methods such as IEquatable<T> or object.Equals overrides.

Asserting That Two References Point to the Same Object with NUnit

If you want to assert that 2 object references point to the same object you can use the SameAsConstraint:

Assert.That(p1, Is.SameAs(p2)); // fail, p1 and p2 point to different objects in memory
Person p3 = p1;
Assert.That(p3, Is.SameAs(p1)); // pass, p3 and p1 point to same object in memory
Assert.That(p3, Is.Not.SameAs(p2)); // pass, p3 and p2 point to different objects in memory

Customizing Equality Asserts with NUnit

There are a number of ways to influence how NUnit performs equality assertions including implementing IEquatable<T>:

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With over 15 years experience, Jason Roberts is a former 5-time Microsoft .NET MVP, freelance developer, writer, and Pluralsight course author. He has written multiple books and is an open source contributor. In addition to enterprise software development, he has also designed and developed both Windows Phone and Windows Store apps.